The publication DE-23 42 743 describes an ice stud designed for winter tires on vehicles. The ice stud comprises an element made of a single material and being rectangular in cross-section. The shape of the ice stud is substantially the same along the whole length of the anti-slip element, and the only exceptions are the narrowing bevels arranged in the inner head inside the tire, the notches made in the stud shank, and the short X-shape of the outer stud head. A stud designed in this fashion is by a slight force pressed deeper in the tire and tends to incline excessively in the tire tread during speed changes, such as during braking or acceleration, as well as during changes in direction, which results in a weak holding power and hence in a weak grip on a slippery road surface. These kinds of ice studs are easily detached from the tire tread during usage. The publication mentions a decrease in the wearing of the road surface as the only objective of the disclosed ice stud.
The publication JP-58-012806 describes a completely ceramic spike for winter tires. The spike is a polygon in cross-section, with the contact surface of the spike tip being particularly polygonal. According to the drawings of the publication, the contact surface of the spike tip is either a sharp-angled quadrangle or an octagon. The spike also includes a bottom flange made of the same ceramic material, with the same shape as the respective shape of the contact surface of the tip.
According to the publication JP-58-012806, the disclosed design is chosen primarily because of the manufacturing technique. But, it is maintained that the strength and grip of the spike are also improved in comparison with a spike that is round in cross-section, but otherwise has the same type of structure. In the publication JP-58-012806, the spike material is mainly composed of aluminum oxide Al2O3, and the durability of this type of material is not sufficient in practice. This type of spike is strongly inclined when driving, particularly if the tire tread is made of a relatively soft rubber, as is the trend nowadays, which means that the grip is remarkably reduced and the spikes may even become detached. If a spike of this type is made of a sufficiently hard, impact-resistant and wear-resistant hard metal, the weight of the anti-slip element becomes remarkably heavy, which means that the wearing of the road surface is intensive and the rubber tread of the tire is easily damaged. The design according to the publication JP-58-012806 makes it difficult to install spikes by automatic devices. The design also results in a swift tearing of the tire tread in the vicinity of the spike when driving, which, as a consequence, can cause the spikes to fall off.
The publication US-2002/0050312 discloses a studded winter tire. According to the publication, the stud has an elongate bottom part with a shape other than round such that the shape has a lengthwise axis. The stud also has an elongate top part other than round such that the shape also has a lengthwise axis. The lengthwise axes of the bottom part and top part are mutually reversed, so that the lengthwise axis of the top part and the lengthwise axis of the bottom part together close an angle other than zero, which advantageously is within the range 65°-115°. The shape of the bottom part and top part of the stud is nearly an ellipse, or an oblong shape resembling an ellipse. According to the publication, this type of stud is shot in the tire tread in a non-vulcanized state by injection tubes, with the cross-sectional shape of the tubes corresponding to the shape of the studs. The studs are oriented within the tread so that in the middle of the tire rolling surface, the lengthwise axes of the top parts of the studs are in a position parallel to the tire axis and the lengthwise axes of the bottom parts of the studs are arranged in the circumferential direction of the tire. At the edges of the tire rolling surface, the lengthwise axes of the top parts of the studs advantageously form an angle of 45° with respect to the circumferential direction of the tire, and the lengthwise axes of the bottom parts of the studs advantageously form an angle of 25° with respect to the circumferential direction of the tire.
When the studded tire disclosed in the publication US-2002/0050312 is made ready, it may function relatively well, but the manufacturing is problematic. Studs designed in this way cannot be reliably turned in the right position in automatic installation machines and the studs may end upside down in the injection tubes. Moreover, studs designed in this way also easily stick to some part of the automatic installation machines. Further, the vulcanization of tires already having installed studs is extremely difficult and expensive and results in a large number of discarded tires in the production process.
The publication WO-99/56976 discloses an anti-skid spike with a hard cermet piece that has a geometric cross-sectional shape, a limited number of symmetry levels and a changing cross-sectional area from the outer head to the inner head such that the hard cermet piece expands towards the bottom flange of the spike. The publication mentions several different cross-sectional shapes of the hard cermet piece, such as a triangle, a rectangle, an ellipse, a semi rectangle, a semicircle, a quadrangle, and an octagon, with all such shapes particularly equal in significance.
As regards the shape of the bottom flange of the anti-skid spike, it is only said that it may be asymmetrical with respect to one lengthwise plane with a length and a width that are mutually different. According to the drawings of the publication, the bottom flange includes two opposite straight sides, either in parallel or at a sharp angle with respect to each other. It is also mentioned that intermediate shapes between these two are possible, but the specification does not offer a more detailed description, only a general remark. Neither of the shapes of the sides of the bottom flange are quadrangles.
The publication WO-99/56976 also recommends the use of a rib in the lengthwise direction of the spike, but without a top bowl.
Further, as shown in the drawings, the longer dimension of the bottom flange of the publication WO-99/56976 can be positioned either in the circumferential direction of the tire, in which case it is suited to urban driving as described in the publication, or perpendicular to the circumferential direction, in which case it is suited to driving on country roads as described in the publication.